1. Field of the Invention
The invention relates to vehicle brakes and in particular to self-adjusting mechanisms for such brakes. More particularly, the invention relates to a brake construction having a low cost self-adjusting strut assembly, which is actuated by a positive action of a push rod, which in turn is controlled by the inward movement of a brake shoe actuating lever upon the outward braking movement of the brake shoes.
2. Description of the Prior Art
Numerous brake constructions having self-adjusting mechanisms incorporated therein have been developed to automatically adjust the brake gap between the brake lining and brake drum to compensate for wearing of the brake lining. Such automatic adjuster mechanisms eliminate the need of a trained serviceman for manually adjusting the brake gap at periodic intervals as heretofore required.
Known self-adjusting brake constructions use various adjuster devices, as well as control means therefor. These adjusters operate either upon outward movement of the brake shoes, or retraction of the brake shoes, with the brake shoes being actuated by either a hydraulic service brake or a manually operated parking brake, or both. Likewise, various types of control cables and linkages are used to actuate the adjuster upon movement of the brake shoes. Cable actuated adjusters use a flexible cable, which operatively interconnects and extends between the adjuster and one of the brake shoes. Outward movement of the brake shoes through the brake gap for contact with the brake drum applies tension to the cable, which in turn advances an adjusting nut or threaded sleeve of the adjuster through rotation of a ratchet wheel or similar device. Such cable actuated adjusters are satisfactory where the particular brake construction enables tension to be applied to the cable during the outward movement of the brake shoes. It is difficult, however, to use a cable actuated adjuster in those brake constructions where the force is applied to the adjuster by the inward movement of the brake shoe or a component thereof due to the length of cable, number of pulleys, etc., required to achieve the necessary change of force direction.
Numerous self-adjusting brake constructions use various specially designed adjuster units to achieve the automatic brake gap adjustment and use various meshing cams, pinion gears, helical adjustment rods, etc. Examples of these constructions are shown in U.S. Pat. Nos. 2,835,354, 3,299,993, 3,299,994, 3,299,995, 3,334,709, 3,507,369, and 3,526,303. Such specially designed adjuster units, however, require specially constructed and machined parts for their successful operation, which increases considerably the cost of the completed brake assembly.
Other types of self-adjusting units use spring means to supply the force which is transmitted from the brake shoe movement to the adjuster, to advance a threaded adjuster rod from within an adjuster sleeve. Examples of such spring devices are shown in U.S. Pat. Nos. 2,695,078 and 3,232,392, wherein a torsion spring and a spring finger provide the adjusting means for regulating the separation of the brake shoes. It is desirable in many brake applications to have a more positive means for applying the force to the gap adjuster, since spring characteristics change due to wear, age, climate conditions, etc., and are susceptible to breakage and maintainence problems.
Thus, the need has existed for a self-adjusting brake construction, which is low in cost, which eliminates expensive specially manufactured adjuster units, which has positive force applying means for operating the adjuster unit to regulate the brake gap, and in which the brake gap regulating force is supplied to the adjuster unit by an inwardly moving brake component through a rigid push rod during outward movement of the brake shoes.